Hot top



Patented May 23, 1939 UNITED STATES PATENT OFFICE HOT TOP ApplicationJuly 6, 1937, Serial No. 152,100

1 Claim.

This invention relates to hot tops .for ingot molds, and moreparticularly to improvements in a detachable hot top adapted to be madeof refractory material.

The emciency :of a hot top and its ultimate accomplishment may be in theratio of the useful portion of the ingot, to that portion which must becropped ofi. Thus a hot top capable of drawing within itself all orsubstantially all of the impurities from the ingot and all orsubstantially all of the porosity or piping which might otherwise existin the body of the ingot, and which concentrates the impurities andporosities into the smallest mass of steel to be cropped, approaches themaximum of efficiency for its intended Particularly where the steel ofthe ingot isvery costly, as, for example, in the so-called stainlesssteels, every pound of steel which can "be eliminated from the partnecessarily cropped. from the ingot represents a corresponding saving inthe costxof manufactur of finished steel.

In the art of pouring ingots with the use of hot tops, it is andunderstood that it is desired to maintain a .head of liquid steel, and asufficient quantity of liquid steel in the hot top for a length of timelong enough to be available to prevent the tendency toward porosity andpiping in the body of the ingot as the outer and lower portions of theingot chill and shrink, and to float up into the crop all .orsubstantially all of the impurities which, by gravity or otherphenomena, may thus be drawn upwardly and out of the body of the ingot.Thusa hot top with relatively great heat insulating properties willmaintain inliquid form the steel within its own body for a longer periodof time than a hot top having poor insulating qualities. By the sametoken, a hot top with the better insulating O, qualities need contain asmaller cubic content of steel, 1. e. crop, since the less efilcient hottop requires a greater mass of steel for the same quantity'of fluid forthe period of time when the fluid head is necessary for properpurification and solidification of the ingot.

Hot tops are subjected to the very high temperatures of molten steelwhen the ingot is poured, and have a very decided tendency to crack andspall under the extreme temperatures to which they are subjected.Spalllng of the hot tops or cracking oil of portions thereof,particularly during the early stages of pouring the ingot, may do'irremedlable injury to the ingot by the deposit of non-metallicsubstances therein. Once the body of the ingot is poured and after thecrop is poured into the hot top, then the cracking of the hot top maypermit an outflow of the molten steel from its body, which mayjeopardize the lives or well being of workmen adjacent the ingot mold,and if the cracking permits such a leak as to lose the head of moltensteel, then all or part of the ingot may be lost as a commerciallyacceptable product by virtue of its containing the defects which theoperation of the hot top, outlined above, was intended to correct. Theloss or damage due to cracking of the hot top is very much more seriousif it occurs in that relatively short period of time before the surfaceof the crop has chilled when the molten steel may escape from the bodyof the hot top. Cracking in a later period, after the crop has chilledenough to form a self-sustaining skin for the fluid content thereof isparticularly injurious where the cracking contributes sub stantially toa loss of the thermal-efiiciency of the hot top. Cracking maysubstantially destroy the insulating as well as other properties ofprior art hot tops now in use.

After the ingot has solidified, there comes a point in the usualpractice where the hot top must be removed or stripped from the crop endthereof, and the facility with which stripping or removal may beeffected is a further measure of the efliciency and advantages of a hottop. Hot tops which crack or spall at points in contact with metal in afluid state will tend to be bonded to the ingot or crop in a manner toimpair the stripping operation, and hot tops, which by theirconstruction or otherwise permit the fluid steel to gain a deleteriousgrip or a locking relation with respect to a part of the hot top, impairthe stripping operation.

It is among the objects of my invention to provide a hot top ofrefractory material capable of bringing about the advantages sought inthe casting of ingots indicated above, and capable of avoiding thehazards and failures found in the prior art hot tops, to which referencehas above been-made. The objects of my invention include the provisionof a hot top in which cracking is substantially reduced or eliminated,and in which the tendency toward cracking is availed of to enhance theoperation of the hot top rather than impair it.

A further object is to provide a hot top having a relatively highinsulating value with adequate structural strength to carry out itsintended thermal and hydraulic purposes combined in a structure whichmay be economically manufactured and used.

A further object is to provide a hot top of stout enough construction towithstand the stresses and strains to which it is subjected intransportation and use, and in which weight and density can becontrolled within desirable limits and which can be extruded accuratelyand easily and fired uniformly.

A further object is to provide a hot top by the use of which thesegregation of impurities from the ingot is substantially complete, andin which that portion of the ingot which needs to be cropped is reducedin mass and amount whereby to increase the useful portion of the ingotwith respect to the crop portion. Within the above objects I provide ahot top which may be easily stripped from the ingot or crop portionthereof.

More particularly, it is among the objects of my invention to provide inthe structure of the hot top a flexibility or elasticity of constructionwhich permits a yielding of those portions of the structure which arefirst put under the stresses of the impact of heat or other forcestending to distort the body of the hot top, whereby the tendency tocrack in a deleterious fashion is substantially eliminated, and relativeexpansion of those portions of the hot top first subjected to heat andfluid pressure is permitted with respect to the cooler portions of thehot top, especially when the temperature differences between variousportions thereof is great.

Other objects and advantages will appear from the following descriptionof one or more exemplary and preferred forms of my invention, referencebeing made to the accompanying drawings, in which Figure 1 is anillustrative view in cross section showing the relationship of a hot topto the upper portion of an ingot mold with the upper portion of theingot and the crop portion thereof shown in relative position after theingot has been cast. Figure 2 is a fragmentary transverse cross-sectionand partially diagrammatic representation of a prior art hot top inwhich are depicted by way of illustration the resolution of certainforces tending to cause the rupture thereof. Figure 3 is a similarfragmentary and diagrammatic View of a portion of a prior art hot top inwhich there are illustratively shown certain of the forces tending toeffect rupture of that style of hot top. Figure 4 is a similarfragmentary sectional view of one form of a hot top embodying theprinciples of my invention. Figures 5 and 6 are similar views ofmodified forms of my invention.

Referring to Figure 1 I have disclosed a fragmentary portion of theupper end of the ingot mold l depicting therein in cross section theupper portion of an ingot-2 having a crop portion 3 embraced in a hottop 4. The hot top 4 is illustrative of the general position and generalformof hot tops known in the art and those in which I embody myinvention in that it is of cylindrical configuration, conformingparticularly at its lower outer surface as at 5 to the upper opening inthe end of them old I, and, as is known, the cylindrical form of the hottops may be circular, square or rectangular depending upon the shape ofthe mold. Lugs 6 or notched corners 6' along with removable orcombustible supporting wedges or blocks, now shown, support the hot topin about the place illustrated in Figure 1, and as the ingot solidifiesthe hot top rests on the shoulders l of the ingot and embraces withinitself the crop 3, which may in the course of cooling develop irregularvoids 8 as are found when the crop portions of the ingots are cut openfor inspection. To measure the effectiveness and accomplishments of ahot top test holes A, B, C and D are commonly drilled in a cut opensection of the upper portion of the ingot in and about the zone shown inFigure 1 to determine particularly whether or not the carbon, manganeseand other chemical elements in the steel are evenly distributed,particularly in this critical part of the ingot. In a comparative testbetween a hot top embodying my invention and a prior art hot top, it wasfound for example that the carbon in the solidified ingot at the point Aamounted to .26 as compared with the content of .22 at point D. Where aningot, poured with a hot top embodying my invention, was similarlyexamined the carbon content of the point A is found to be only .24 asagainst a carbon content of .23 at point D. The'advantage measured bythis test was that with using my hot top, it was shown that thesegregation of impurities above the point A was much more complete thanit was with the use of the prior art device. For the same reason theextent of the crop necessary to be cut down to the point in the ingotbelow which the distribution of carbon, for example, was uniform, wasvery much less when my hot top was employed than when the prior art hottop was used.

In Figure 2 I have shown in cross section a fragmentary portion of acurved wall of hot top of solid cross section, according to the practiceof the prior art, and it will be appreciated when the hot metal bearsagainst the inner wall |0,the same is heated very rapidly, and that highcompressive forces are created in the inner portion of the wall of thehot top, as I have indicated by the arrows H. These forces incompression, measuring the tendency of the inner wall of the hot top toexpand, are resolved into radial forces l2 acting through the body ofthe wall, and are resistant by forces in tension [3 in the outer portionof the wall. Since the tensile strength of fire clays and otherrefractory materials from which such hot tops have been made isrelatively small, and since the heating of the inner surface of the hottop is very rapid, the inevitable result of the use of such hot tops isthat fractures will occur roughly along the line I5, as indicated inFigure 2. Moreover, since the wall of the hot top is solid, the tendencyto fracture is not limited to any plane of direction, and fractures mayextend vertically or horizontally or in combinations of those directionswith the disadvantageous results discussed above. Such hot tops arefrequently bound with two or three wire hoops which add about 5 to 10 tothe cost of use of each such hot tops without curing the inherent evilthereof.

Moreover, the compression forces ll build up in amount very rapidly,particularly where the wall of the hot top is dense and thick and solidas shown in Figure 2, and these excessive compressive forces tend tocause spalling of fragments from the inner surface I!) of the hot topwhich may add non-metallics to the ingot and impair the stripping of thehot top therefrom. The more firmly the inner annular portion of the wallof the hot top is held against expansion, the more rapidly do thestresses therein build up. Thus the thicker and denser solid walls seemto crack and fracture more quickly and with more disastrous results thando the thinner and less dense ones, However when powdered coal or othercarbonaceous material has been added to powdered or pulverized clay inthe process of making solid wall 110? tops, the density has beenreduced,

but it has been most .dimcult if not impossible to burn the carbonaceouscontent out of the, midportion of thick walls, whereby when such wallscrack, the free carbonaceous material is exposed to enter, into the bodyof the ingot. Moreover, the difficulty in burning out carbonaceousmaterial from thick and solid walls leaves the resultant density andstructural characteristics uncertain and lacking in uniformity. Byproviding voids in the walls of my hot tops to be presently described,and by restricting the wall thicknesses, I am enabled, among otherthings, to burn out all the carbonaceous material that may have beenadded and thereby obtain and control the density and other structuralcharacteristics of the various parts of the wall within substantiallydefinite and desirable limits. Furthermore in carrying out the objectsof my invention, I provide in the forms of my hot top, presently to bediscussed, a certain freedom of the inner annular portion of the hot topwith respect to the balance thereof whereby it can give or yield withthe resuit that the stresses therein are not permitted to become great,and the damage resulting from excessive stress in the more criticalportions of the hot top is materially reduced if not substantiallyeliminated.

In Figure 3 is disclosed another form of prior art hot top in whichrelatively large voids l6 are formed between the inner wall l1 and theouter wall i8, which walls are joined by radial webs 9. It has long beenknown to provide relatively large voids both-in the upper ends of ingotsmolds and in detachable hot tops. Where such hot tops are detachable andparticularly when made of refractory material, there are variousdisadvantages, one of which is that the tendency for such hot tops tocrack while the crop portion of the ingot is fluid is substantiallythe'same as that'in a l solid hot top, i. e. the expansion of the innerwall I! creating forces in compression I exert radial forces I 2 in thewebs H), which in turn are resisted by forces in tension I3 in the outerwall l8 and also by shear stresses in the zones indicated by the lines|A and 5B. The result is that the tendency of such voided hot tops tofracture is great along the line I5, because the stresses and strains ofboth tension and shear are combined in the zone of the web l9, andexperience demonstrates that these hot tops split from the outer wallthrough the radial webs and inner wall with disconcerting frequency.Spalling as at S can be expected to occur in this form of hot top forthe same reasons discussed in respect to Figure 2,

although the same may be less in degree.

According to the precepts of my invention, I

walls or zones of my hot top a structure having a cushioning effectbetween the rapidly expanding inner wall or zone and the relatively coolouter wall or zone, Within the same principle, I provide a web structurebetween inner and outer zones orwalls of a voided hot top in which thetendency to fracture may be directed into the webs themselves, wherebyto leave the inner wall and outer wall or zone intact, and to retain inthe hot top all of its qualities, both thermal and hydraulic, until suchtimeas the intended work of the hot top has been accomplished.

Moreover, within or beyond the elastic or yieldable portions of the wallI am able to develop the insulating qualities of the hot top to a greatmeasure because of the compensation provided for the difference inexpansion between those portions. In effect, I am enabled to allocatethe hydraulic function of the hot top essentially to the inner wall anddevelop the thermal and mechanical function in the outer portions of thehot top to an extent which has heretofore been quite impracticable ifnot impossible.

In Figure 5, for example, a hot top embodying the principles of myinvention may have an inner surface with adjacent annular wall portion20 and outer annular wall portion 2|, the two walls being joined by webs22, which lie in part parallel with the inner and outer walls and definenarrow voided portions 23 having short radial parts and relatively longcircumferentially extending parts as shown. When the molten metal heatsand expands the inner surface of the wall 20, forces in compression asat H" are created, which in turn are resolved into radially actingforces l2", but in this case these radial forces l2 can only be opposedby offset radial forces |2A resulting from the tension in the outer wall2| indicated by the arrows at IS". The result is that a couple tends tobe established by the forces l2 and I2A, and the web 22 is subjected tobending moments and shear stresses with the result that the Web willgive somewhat or fail before transmitting destructive forces to theouter annular part 2| of the hot top. This will permit expansion of theinner annular portion of the hot top 20, thereby relieving the innerportion from its tendency to crack or spall under its own compressivestrains and relieving the outer portion from stresses tending to ruptureit in tension. Of course the flexibility of the webs 22 in refractorymaterials is limited, but by disposing the webs as shown in Figure 5,that is generally parallel to the inner wall of the hot top, and makingthe webs of less strength in their resistance to bending or shear orotherwise than have the inner wall in compression or the outer wall intension, for instance, then I can be assured that the webs 22 yield orfail, as for example about or along the line 24, before there is anydeleterious impairment in the function and operation of the hot top as awhole. Furthermore, it will be seen that even after one or more of thewebs 22 fracture as along the line 24, or at any part of its length,there is no substantial change in the voided cell structure or otherwiseof the whole hot top, whereby it continues its whole function andoperation throughout the whole period of time when the ingot and thecrop is solidifying.

As shown also in. Figure 5, I am able to make the inner wall 2!! of thehot top relatively thin, about where the whole wall may be from 2" to 3"thick, whereby the whole of this inner wall portion of the hot top canmore nearly come to the same temperature at the same time, and itstendency to crack or spall for the reasons given in. connection with thedescription of Figure 2- is very materially reduced.

Furthermore, the tendency of the inner wall 20 to crack is confined to avertical direction by virtue of the vertical arrangement of the adjacentWebs and voids, and even if the inner wall 29 should crack under its ownstresses before the adjacent webs failed, then the forces acting throughthe webs would continue to hold the portions of the inner wall onopposite sides of the crack in a compressive relationship, therebytending to hold the crack substantially leak-proof. In any event, thetendency of an inner wall to crack is greatly delayed in point timebecause of its relative freedom to expand, its relative freedom fromexcessive internal stresses and because it is not necessarily restrictedto a deleterious density controlled by manufacturing limitations.

In the course of ordinary manufacture as by extruding the hot topsthrough auger machines, well known in the art of making hollow tile, theordinary errors in such manufacture may cause a reasonable lack ofuniformity in the thicknesses of the webs, whereby the thinner oneswould naturally tend to yield or fail before the thicker ones. Thiscondition might tend to induce cracking in the inner wall adjacentcertain webs, but even in this case, as indicated above, the tendency tocrack is long delayed past the critical stage when the metal is in thefluid state, and in no event is there any tendency for a crack to formtraversing the whole distance from the inner surface of the hot topthrough the outer wall, the tendency being to initiate cracking, if any,in the webs, and to postpone deleterious cracking, particularly in theinner wall, until after the critical period has passed. By virtue of theflexible or yieldable connection between the inner and outer walls, andthe insulating effect of the voids therebetween, the tendency towardcracking of the outer wall is substantially eliminated, and with it thehazard of a complete break-through or leakage of the hot top is alsosubstantially dispensed with. The tendency to crack in the outer wall isnot only very greatly reduced, but is much longer delayed by virtue ofthe insulating and yielding effect, particularly in the voided portionsof the hot top; the delay being such that the hot top will have had timeto perform substantially all of its work before any deleterious Xcracking or rupture of any part of the outer wall may take place.

As depicted in Figure 5, I prefer that the voids 23 be relativelynarrow, preferably varying from about 1%" or less to about 1 in thoseparts near the inner wall to from about to about 5%" in those partsnearer the outer wall. The connecting webs may in their thinner portionsbe about A; of an inch thick, and may be somewhat thicker where theyjoin the inner and outer walls respectively to facilitate extrusionthereof. Preferably the voids are relatively long circumferentially (andextend the full height of the hot top, see Fig. 1) but are quite narrow,whereby great insulating effect is gained, particularly by themultiplicity of such voids across the direction of the flow of heat, andby virtue of their being narrow they tend to exclude the upward flow ofmolten steel from the top of the ingot along the shoulder I, see Figure1, when the main body of the ingot is poured. Since the steel adjacentthe shoulder 1 tends to chill and form a solid or plastic coatingbeginning at the point of contact with the mold wall, and since thesolidification moves from the outside to the inside of the ingot, Iprefer, as indicated above, to make the voided portions of the hot topnearer the center of the hot top narrower than the voided portions,whose lower ends lie closer to the walls of the mold. In either event,whatever fluid steel tends to enter the lower extremities of thesetop asdo voids of much greater width, but by the use of narrow voids I amenabled to use more of them and obtain an insulating value increasingroughly in proportion to the number of voids interposed in the radialpath of the flow of heat, and as indicated above also have gained otheradvantages including restraining the movement of fluid metal upwardlyinto the voids when the body of the ingot is first poured.

It will also be observed in Figure 5 that the flow of heat by conductionin the solid parts of the hot top, as from the inner wall through theweb 24, has a much longer path to traverse than any straight radialpath, whereby the resistance to the flow of heat through the solidmaterial is impeded not only by the length of the path but also by itsrestricted cross sectional area. It will further be observed in thisconnection that where the webs fail by cracking, as in and about lines24 and 25, the flow of heat through the broken webs is furtherrestricted whereby the insulating value of the hot top as a whole isincreased after the webs have been fractured. From this point of View myhot top has its insulating value enhanced by fracture of the webs,whereby I take advantage of the tendency of the hot top to fracture notonly in relieving the stresses and strains therein, but also inincreasing the insulating value thereof.

In Figure 4 it will be seen that the principles of my inventiondiscussed above are carried out in a similar way in that the innerannular wall portion is insulated from the outer annular wall portion 3|by a double row of narrow circumferentially extending voids33 and 34,and is connected therewith through web portions lying generally parallelwith the inner and outer wall portions, and being preferably reduced inthickness as at points 36, whereby the yielding relationship between theinner and outer portions of the hot top is provided, and the tendency tofracture is concentrated in and about the points 36 in the webs 35. Theoffset disposition between the radial forces of and opposing expansionof the inner annular wall of the hot top is also maintained, and theoperation and advantages, explained more fully in connection with theform shown in Figure 5, will also be found in the form shown in Figure4. In Figure 4, I prefer that the voids 34 be arched from a state ofparallelism with the inner voids 33, whereby to more sharply reduce thethickness of the webs 35 at the points 36 to concentrate the tendency tofracture at these points, and also to permit an easier flow of the claystream during extrusion, particularly in and about the points 31 underthe crowns of the voids 34 as viewed in Figure 4. The relative sizes ofthe webs and voids may preferably be substantially the same as thosereferred to in connection with the description of Figure 5, although bythe arching of the webs 34 it is feasible to bring the thickness of thewebs 35 down to about an A; of an inch, if that be desired, at thepoints 36 without any undue awkwardness in the extrusion process. Theinclined relationship of the ends of the voids 34 with the voids 33 alsotends to compensate for involuntary movement of the cores in theextrusion die in that undesirable mergers of the adjacent voids areavoided.

In Figure 6 I have shown a further modification of the form of the wallstructure of a hot top, in which my invention may be advantageouslypracticed, and in which the inner wall portion 4|! is spaced from theouter wall portion 4| by three rows of voids 43, 44 and 45. The innerand preferably thinner voids 43 are closer to each other as at 46, andthereby further restrict the flow of heat in the solid portions of thehot top; the arched voids 44 with the intervening web portions 41 beingpreferably substantially of the shape and relationship described inconnection with Figure 4, and the outer voids 45 preferably beingsimilarly spaced with relation to each other as are the inner voids 43thus reducing the web portions therebetween as at 4B. In thisrelationship it will also be seen that the web portions are disposedgenerally in a parallel relationship with the inner and outer wallportion, that the yielding relationship between the inner and outerportions is thereby provided, and that the other characteristics ofoperation and the advantages discussed particularly with respect toFigures 4 and 5 are also obtained in this modification, the insulatingvalue of the hot top as a whole being enhanced by the additional row ofvoids.

With the use of hot tops embodying my invention, including those in oneor another of the forms above described, I have already indicated howthe segregation of impurities in the ingot is greatly improved by theuse of my improved hot top. In the same comparative test the hot top inwhich my invention was embodied had the over-all thickness of its wallsincreased whereby to have one inch less internal diameter than the priorart hot top with which it was compared. Both hot tops were used on moldsof the same size and both hot tops fitted into the upper end of themolds with substantially the same clearance. Both hot tops were filledto substantially the same level when the ingots were poured. The resultwas that not only was the segregation very much better as I have shown,but also the mass of metal in the crop portion of the ingot throughwhich these better results were obtained was reduced by a little morethan 13%, that is in proportion to the fluid content of the hot top. Hadthe prior art hot top been merely increased in wall thickness thetendency to deleterious cracking would have been at leastproportionately increased. With my hot top with the greater over-allWall thickness, the insulating value was increased in much higherproportion than the increase in wall thickness, its weight was increasedless than the proportionate increase in wall thickness, and the tendencyto deleterious cracking eliminated.

While I have spoken of certain advantages to be gained in reducing thedensity of my hot top as through the use of powdered coal, it should beappreciated that other of the advantages persist regardless of the exactdensity and that my invention in this regard is particularlyadvantageous in facilitating uniform manufacture and satisfactoryresults throughout a wide range of densities that may be chosen to meetwidely varying demands and conditions.

While in the foregoing I have illustrated and described a preferred formand certain alternative forms in which my invention is embodied, variousand perhaps numerous changes and modifications will occur to thoseskilled in the art without departing from the spirit or primary teachingof my invention, and while I have indicated a preference for certainforms and structural details of the hot tops embodying my invention, Ido not care to be limited thereto or in any manner other than by theclaims appended here, when construed to embrace the equivalents to whichI may be entitled in view of the state of the prior art.

I claim:

A hot top having inner and outer annular wall portions embracing avoided portion therebetween, said voided portion comprising a pluralityof non-radial, axially straight and continuous webs joining said wallportions and having parts extending generally circumferentially of saidhot top, said webs and adjacent wall portions defining a plurality ofnarrow, circumferentially overlapping, axially straight voids eachextending the full length of said hot top and together encircling theinner wall portion thereof.

ARTHUR C. ES'I'EP.

